1. Field of the Invention
The present invention relates to probe cards for high-frequency test signal transmission for testing electronic devices of a semiconductor wafer and more particularly, to a probe card having adjustable high-frequency signal transmission paths for enabling output of synchronous high-frequency test signals from a tester to devices under test.
2. Description of the Related Art
As electronic products become increasingly high-speed operation and integration of processing functions, semiconductor wafers are mostly formed of digital chip circuits for high-speed and high-frequency applications. Therefore, single-chip circuits tend to have multiple sets of circuit inputs. After through internal multiplex and synchronous processing, you can make the output of a single chip circuit be integrated with the functional requirements of a variety of electronic products. When a probe card probes high-speed processed digital chip circuits in a wafer-level testing, the probe card is used as a space transformer between the tester and the chip circuits. The transmission frequency of the test signals in the probe card not only must match the operating frequency of the chip circuits, it also must to let multiple input pins of the chip circuits to synchronously receive the test signals, avoiding signal output distortion to affect test quality due to delay of some input signals.
Taiwan Patent Publication No. 200537654 disclosed a semiconductor package design entitled “High Electric Performance semiconductor Device”. In this design, the package uses packaging components to serve as space transformer for the pins of the chip circuits. This design also faces the synchronization and integrity of signal transmission of chip circuit signals. When it is necessary to conduct the pins of chip circuits having a relatively fine pitch to package contacts having a relatively larger pitch, the unequal lengths of bond wires will result in the drawback of differential signal inconsistence. Although this patent teaches the arrangement of same length lead wires to let the pins of the chip circuits be electrically connected to the package contacts through the lead wires by means of a wire bonding structure having approximately the same length. However, there are also unavoidable mechanical errors in the control of wire bonding.
In the fabrication of a probe card for wafer-level testing, even all module structures of the probe card have been configured into a consistent transmission structure subject to the defined high frequency characteristics, differences of high frequency signal receiving timing in the module structures may still occur after the module structures have been assembled because high frequency signals are highly sensitive to environments of transmission structures. For example, in a probe card for testing wafers of 300 mm, each single transmission line extends from the periphery of the probe card to one respective probe at the center. A minor total signal path difference between different transmission lines, for example, 1 mm, will cause a time difference of several tens of picoseconds between the received high frequency signals in high frequency chip circuits operated in Giga Hertz. Installation errors of different transmission paths of a probe card may be unable to output signals to chip circuits synchronously. Therefore, most commercial probe cards cannot actually meet high frequency test conditions for chip circuits, constraining wafer test engineering to limited high frequency bandwidths. If the probe card circuit is completely laid on the circuit board within the board structure, of course, the length of all transmission lines can be precisely controlled during the integrated circuit layout process; however, it can only be applied to test a specific wafer. After module engineering, the specifically designed probe card can simply allow sintering repair for short circuits and broken circuits, and is difficult or not permitted to adjust signal transmission synchronization.
Taiwan Patent No. M361631 disclosed a probe card design, entitled “Cantilever Probe Card”. According to this design, this cantilever probe card is a probe card module structure of the assembly of external circuits and a standard printed circuit board for probe card. It provides an added flexible circuit board, and signal contacts at two opposite ends of the flexible circuit board. By means of cutting the flexible circuit board, the wire length can be adjusted subject to the location of any signal contact. However, in a high frequency signal transmission structure using, for example, high frequency transmission lines or signal transmission lines of differential signal pairs, test signals are almost completely transmitted through the transmission wire materials in and/or around the probe card to the probes at the center of the probe card. After module engineering, the lengths of the transmission lines can simply be adjusted using a mechanical cutting method. However, to a transmission line structure having the characteristics of low impedance and large diameter, the precision of micro adjustment using a mechanical cutting method may have an error about 1 mm. Therefore, in actual practice, conventional probe cards for high frequency test signal application are all limited by probe card module fabrication errors, unable to overcome the problem of signal asynchronization during transmission of high frequency signals through the probe cards to chip circuits.